HILL AIR FORCE BASE — Work by defense and industry partners here returned more than 80 F-16 Fighting Falcons to the skies after they were grounded in 2014.

An intense, eight-month effort to structurally reinforce F-16 aircraft began in July 2014 when technicians from the 56th Maintenance Group at Luke AFB, Arizona, noticed cracks in the left canopy sill longerons of four of the unit’s two-seat F-16s. 

By August 2014, more than 80 aircraft were grounded and repair planning started.

The repairs were completed shortly before the end of April 2015, thanks to a combined effort by teams from the 309th Aircraft Maintenance Group, F-16 System Program Office, Lockheed Martin, the 309th Commodities Maintenance Group, the Air National Guard, the Defense Logistics Agency and others.

The discovery at Luke led to an Air Force-wide inspection of all 157 F-16D models; 82 were identified with cracks. Luke had 32, the most aircraft affected at one base. The longeron is the area that the canopy rests on, immediately to the pilot’s right or left when seated in the cockpit.

“The canopy sill longeron is a major structural component,” said Lt. Col. Chris Goad, Materiel Leader, F-16 Programs Branch, F-16 System Program Office. “The work increased to 83 aircraft because we had another one break while we were doing the fixes. Our specific repair fixed 79 aircraft.”

Air Force and Lockheed engineers developed a model of what the end repair needed to look like, then worked with the 309th CMXG to create aluminum and steel straps that would reinforce the aircraft.

The 533rd Commodities Maintenance Squadron New Manufacturing Flight in turn created computer drawings from the model in its programming office, then had a prototype made from the drawing using a 3-D printer operated by the 309th Maintenance Support Group. Once the prototype was fit tested, the first part was machined from a 120-pound solid block of aluminum by the 532nd CMXG.

“It’s not your standard aluminum that you can go down to Home Depot and buy,” said Kent Law, 532nd CMXG Industrial Programmer for New Manufacturing. “This is a special aircraft aluminum that comes with certification from the vendor. It’s accountable from the mill to the vendor to us, and we have to maintain the records.”

The resulting “prove-out” part — 106 inches long, 10 inches wide and 3 inches thick — was laser scanned by the 309th MXSG and matched to the model for verification.

After the initial work was completed, a list was created to standardize the set-up, operating sequence and tools needed. Included were 11 tools and nearly 120 steps that detail the machining requirements.

At first, it took more than 40 hours to machine each strap, but that was reduced to 35 hours as some lines and cuts were found to be unnecessary.

“We ran two 10-hour shifts, six days a week,” said Darren Ketchell, Production Supervisor for New Manufacturing. “We started with some 24-hour runs, but found we could accomplish it in six days at 20 hours. We gathered people from all over into our building — four programmers that helped us out a ton, and 16 production machinists. We have one of the highest skill sets in the state with our machinists — they are a hard-working bunch.”

After consulting with SPO engineers and working on two aircraft at Hill AFB to validate and verify what the repair involved and what tools were needed, an eight-man team from the 309th AMXG Expeditionary Depot Maintenance Squadron headed to Luke.

“We had to take out a lot of fasteners on the canopy sill longeron itself, and on the outside of the fuselage skin there,” said Master Sgt. Thomas Hartley, EDMX section chief. “We worked over those holes and put stronger fasteners into place. There are also two different straps — there’s a steel strap that runs along the top of the canopy sill longeron, and one on the side.

“We fastened it all together. Basically, it’s just beefing up the areas that cracked.”

Early forecasts estimated the work at Luke wouldn’t be finished until March, but the EDMX team finished that portion before Christmas. The speedy completion was attributed to help from base production teams.

“The production lines were actually doubled and aircraft was stacked up in the hangars,” said Senior Master Sgt. Davick Hansen, EDMX Superintendent. “Production teams prepared the aircraft before our team needed it, then our guys would just move their way down the line — it was pretty awesome. And to think there were only eight people doing that for 34 airplanes. It was definitely a team effort.”

The first aircraft took six days to repair, but once the process was perfected, the teams were able to fix others in just 3 1/2 days.

“It was just a matter that we were dedicated to go out there and do 12-hour shifts, six days a week,” Hartley said, “but once we learned the repair process and started streamlining everything, we got down to normal shifts. By the last month we were there, we were cranking them out faster than what we anticipated.”

The work started by the EDMX team led to repairs being completed in other areas where the workload wasn’t as large. By the end of December, 64 aircraft at Luke and other bases were completed.

“Once we got the proper tools, we were able to implement work among five depot teams supported by AMARG and ANG personnel at Luke, Davis-Monthan, Kelly, Edwards, Nellis, Misawa and other bases — 10 bases total,” Goad said. “Our initial focus was at Luke because that was where they had the most grounded aircraft.”

The repair is good for 6,000 flight hours and can also be used as a preventative repair. As other F-16s go through scheduled depot maintenance, the canopy sill longeron repair will be installed to prevent further cracking, Goad said.

“It’s not a highly expensive repair. The material itself is not exorbitant,” Goad said. “The total repairs cost $1.3 million, which includes material, depot installation and depot field team travel expenses.”

Goad, Ketchell, Law and Hartley were quick to credit others for the success — Jim Pruin and Joe Gerling, program managers; Bryce Harris and Dr. Kim Jones, Aircraft Structural Integrity Program engineers; Mike Shaw and Beau Jensen, Structural Engineers; Chad Brown, equipment specialist; the Bldg. 510 machinists who milled the parts; and Arnie Leighton, production controller, who ordered nuts and bolts.

“It was amazing — from the identification in late July and TCTO, inspection guidance given at the beginning of August to the bulk of repairs done by the end of December — this was a really good accomplishment,” Goad said. “People thought it was going to take longer than it did to get through the process, to get all the parts identified, material bought and produced, tooling delivered, get the depot teams in place.

“It was a lot of work and every day was a ‘fire,’ but it worked out well overall. It was a great display of teamwork across the Air Force and within Hill AFB Air Force Sustainment Center and Air Force Life Cycle Management Center units.”